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The front femora and tibiae are nothing like long-spined enough for spinimanum (which has the rows of long, slightly curved spines beneath the respective joints). I'm not certain it is a Scathophagid, as the angle makes the features hard to discern.
My Flickr photos...
any chance of finding the species with a specimen? hyalipennis, for example, what might one look for to rule it out, or in
latest pics and diptera videos
Although some sciomyzid flies are distinctive, I'm afraid Tetanocera is one of the harder genera, with species ID often relying on details of the male genitalia. Dissection may not be needed, but a specimen under a microscope will be in most cases.
The recording scheme is working on a new key to the UK species, but not sure if anything is available yet - see:
Entomologist and biological recorder
Lat/Lng: 51.5, -3.1
OS grid ref: ST2589